I can see how reading a weekly round up of the thoughts and activities of a sports person might be interesting, but what about the general opinion type ones in newspapers ?
All newspapers seem to have them, both in print and on line.
The only point I can see is that the on line ones are good click bait.
Blogger says something controversial, cyclists, or whoever it they’ve upset this week post links on cycling forums, web site gets more traffic, they then sell more advertising space.

Potential audience of say, 2 billion people.
Costs, effectively free.

blogs:

Good – Freedom of speech for all/when they’re truly interesting and updated regularly you can get completely immersed in them

Bad – Most of them appear to be set up by people with an agenda/can’t get over the fact that they’re not 16 year old goths anymore and use it as an online diary or moanthon/people who think they’re photographers because they once bought a camera

Costs, effectively free.

Not sure the person writing the blog would agree with that.

I get the feeling that newspaper blogs are a bit of a lead-in to being able to write for the newspaper proper. And, as MTG suggests, click fodder for saying something absurdly controversial with deniability from the main paper.

Don’t bother (usually) with newspaper ones, but geeky tech ones are often an excellent source of information, indeed they’re often the only source of information…